Hello. First thing you need to check is the charging. And also you will need to check the aux battery for proper voltage as well. This battery is in the trunk. Make sure that both batteries have voltage greater than 12.4 and also make sure the front battery is charging at 13.0-14.6 no higher or lower. Let me know. Thanks. Lou

Thanks Lou, I already did that a couple times. So has a friend, all charging seems fine. I just didn't want to have to type everything I already tried (would have been a mile long question). Although rear battery is also charged, will say surprised to see it's usually about a volt less. Engine on: Front @14.45V, Rear: @13V. Eng Off: Front: @12.7V, Rear: 12.9V. 6 months ago, inadvertently left a trickle charger on vehicle with engine on and that same battery message came on. Shut down, engine and removed trickle charger, and the car worked fine until now. Tried disconnecting batteries, to reset, then reconnecting and let sit for 4 Hrs to Learn (I don't know, but am told apparently the battery sensor is supposed to learn). Problem still occurs.

No luck yet. Did load charge both batteries, they seem fine. Saw on the Benz forum there is an order to disconnecting and reconnecting the batteries. did that per the order (disconnect rear first), Reconnect the front first.

Ok on a lot a models the battery sensor was giving false battery information. It's the sensor on the negative terminal. This could be the issue. Do you have a way to check codes ? That will ultimately be the best way to see what the computers are having issues with. If the voltages are always correct then I would suspect the IBS (intelligent battery sensor ) let me know what you think.